Iarnród Éireann has said it hopes to start the first scheduled commuter services through the Phoenix Park by the end of the year.
The company has begun a two-week public consultation on the new routes, which could carry up to 3,500 commuters from Kildare into the IFSC and access the south city at Connolly and Docklands stations.
An Iarnród Éireann spokesperson said market research had shown there is "an appetite" among Kildare commuters for the new services and its hoped the extra trains will encourage more to switch from car to rail travel.
A signalling upgrade of the tunnel line has been completed at a cost of nearly €14m.
The proposed extra services will include seven new services at morning peak time from Newbridge/Hazelhatch to Grand Canal Dock and eight new returning services at evening peak hours.
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The new rail route would not stop at Heuston but existing services to it would be maintained and outer commuter services could connect with the Phoenix Park tunnel route from Carlow, Portlaoise, Kildare and Athlone.
The Phoenix Park tunnel was previously used mainly for shunting trains between Connolly and Heuston stations and for occasional passenger services for special events such as All-Ireland finals.